Assembly element for tow component parts of a device

ABSTRACT

The assembly element is mechanically connected to two component parts of a device ( 2 ) at least once the device is assembled. A shape-memory metal element ( 6   i   , 7   i ), is provided as the assembly element, the metal element having a first form during assembly of the device ( 2 ) and a second form, which assures the mechanical connection between the two component parts ( 3   a   -3   d   , 4   a   -4   c ) of the device, when the device is assembled. The second form is memorized by the shape-memory metal element before assembly, by its shape-memory properties.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the 35 USC 371 national stage of international applicationPCT/DE01/046140 filed on Dec. 10, 2001, which designated the UnitedStates of America.

FIELD OF THE INVENTION

The invention relates to an assembly means for two individual parts of adevice, the assembly means, at least in the assembled state of thedevice, being connected in a positively locking manner to the twoindividual parts of the device.

BACKGROUND OF THE INVENTION

Examples of known assembly means which can be used to produce inparticular a positively locking and if appropriate a nonpositivelylocking connection between individual parts of a device are screws,rivets or clamps.

The increasing integration density involved in the development ofcomponents and mounting technologies in particular in the field ofsemiconductor electronics is leading to evermore powerful, smaller andmore lightweight modules or corresponding devices. In addition to thehigh quality demands imposed on the construction of devices of thistype, it is also desirable for the device production and assembly to beautomated as far as possible for cost reasons. In this context, aproduct design with increasing miniaturization encounters the problemthat the space available for the assembly and connection means for theindividual parts of these devices is becoming ever smaller and/or theconnection points are becoming ever more difficult to gain access to.

Moreover, statutory regulations mean that the manufacturers of certaindevices are often forced to take back old devices and to provideequipment for treating or processing these old devices. Therefore, forcost reasons the devices have to be easy to dismantle.

Since the manufacturers of many devices were not previously obliged totake back old devices, requirements relating to the dismantling of theindividual parts of these devices were only a minor factor in productdevelopment. In particular the technologies for circuit carriers/circuitmounting are in a state of flux; product developments are increasinglybased on the innovative large scale integrated technologies, such asflip chip, ball grid array, all layers interconnected via holestechnologies, etc. With new technologies of this type, it is desired toachieve high integration densities. The result of this is that thevolume available for the assembly, connecting and joining technology iscorrespondingly reduced. With conventional connecting technologies, suchas screw connections, riveted connections or clamped connections, it isbecoming increasingly difficult to construct and assemble or dismantleminiaturized devices of this type.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide anassembly means for the assembly technology in particular of miniaturizeddevices of this type which makes it easier to put together and/ordismantle at least two individual parts of a device even at inaccessibleand/or miniaturized connecting points. In the assembled state of thedevice, the assembly means is to ensure a mechanical connection betweenthe individual parts which are at least to be connected.

According to the invention, this object is achieved through the factthat the assembly means includes at least one memory metal element or isformed by this element which, in the assembly state or in the assemblyphase (=phase during which the device is being put together) of thedevice, takes a first form and which, in the assembled state of thedevice, takes a second form, which is responsible for ensuring themechanical connection between the individual parts of the device andwhich has been imparted to the memory metal element, making use of itsmemory property, prior to assembly of the device. In this context, amechanical connection is understood as meaning any desired positive lockbetween each of the individual parts of the device which are to beconnected produced by means of the at least one memory metal element.

The advantages which are associated with this configuration of theinvention are to be considered in particular to lie in the fact that thedemands imposed on various phases of the life of the device can befulfilled by using tailored application-specific materials properties,it being possible to integrate functions such as optimization of thespacing or damping of vibrations in the element by using at least oneelement with memory properties. Instead of having to use complex spacersand/or relatively inaccessible screw/rivet/clamping or snap-actionconnections, all of which require additional process steps in assemblytechnology, the inventive use of memory metal elements after assemblyensures the desired positive lock, and if appropriate also a nonpositivelock, in a simple manner by setting the second form on the basis of thememory effect. This setting of the second form takes place in a mannerwhich is known per se, i.e. generally by means of a targeted heattreatment.

Advantageous configurations of the assembly means according to theinvention will emerge from the dependent claims.

For example, in the assembly state of the device, it is particularlyadvantageously possible for the mechanical connection produced by meansof the at least one memory metal element at the same time to be anelectrical connection and/or a thermally conductive connection. This isbecause measures for making contact and in particular for dissipation ofheat to in relative terms larger heat exchange surfaces are veryimportant in particular in highly miniaturized devices. The assemblymeans according to the invention is able to satisfy correspondingdemands in a simple way.

Furthermore, it is to be considered advantageous if the at least oneelement having the memory property is in the form of a spring, a strip,a bolt or a rivet. Components having application-specific forms of thistype may advantageously be positioned between the individual parts whichare to be connected even within a small space.

In this case, the memory metal element may advantageously be rigidlyconnected to one of the individual parts of the device which are to beconnected, for example may be soldered to this individual part. Solderedconnections of this type can advantageously be performed at the sametime as soldering of further components of device or of an individualpart of the device. This is highly advantageous in particular in thecase of highly miniaturized devices.

Furthermore, it is to be considered advantageous if, to dismantle thedevice, at least one nonpositive lock between the memory metal elementand at least one of the individual parts of the device can be eliminatedby spatially detaching one of the individual parts from the element.Since the positive and/or nonpositive lock between the element and theindividual part to be connected is generally performed only by theelement being placed onto this individual part with the exertion of acompressive force, which may only be slight, simple dismantling ispossible without this individual part having to be damaged or destroyed.In this way, it is even possible to reuse valuable individual partsand/or the elements with a memory property for the same or similarapplications. Also, this allows dismantling or self-destruction to takeplace without any mechanical intervention with regard to connectionbetween the element with a memory property and the individual part whichcan be detached.

The at least one memory metal element can preferably be provided as aspacer feature between two individual parts of a device. During deviceassembly, for example within a housing, the individual parts of thedevice then merely have to be loosely joined together or placed on topof one another; final positioning within the device then takes place byactivation of the second form of the memory metal element in question.

However, it is also possible for the at least one memory metal elementto be designed as a clamping feature, which can be used to create aclamping connection between the individual parts of the device which areto be connected.

To activate the second form of the at least one memory metal element,the latter may be assigned a heating means. This may advantageously be aheating current passing through the memory metal element in question ora heating device outside the memory metal element. In this case, it isnot necessary for a plurality of memory metal elements to be activatedsimultaneously.

The at least one memory metal element may advantageously at leastpartially comprise a TiNi or NiMn or CuAl alloy, with at least onefurther alloying partner being present if appropriate. The excellentresistance to corrosion of the abovementioned materials represents aparticular property which allows the element according to the inventionto be used in a mobile vehicle, such as for example in an automobile, orallows some other decentralized, mobile use, including in anenvironmentally polluted atmosphere. This therefore opens up thepossibility of production taking place in an atmosphere of this type.

Further advantageous configurations of the connecting means according tothe invention are given in the remaining claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To further explain the invention, reference is made below to thedrawing, which diagrammatically depicts an advantageous embodiment of adevice with assembly means according to the invention and in which, ineach case in a perspective view:

FIGS. 1 and 2 show two different assembly states of a correspondingelectronic device, and

FIG. 3 shows a possible way of dismantling this device.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the figures, corresponding parts are provided with identicalreference symbols.

Memory metal elements according to the invention make it possible toproduce a positively and if appropriate also nonpositively locking,generally at least partially releasable connection to or betweenindividual parts of a device, preferably an electronics device. Thedevice may in particular be a means with a high degree of integration ofits components, such as for example a mobile telephone, a notebook orcontrol electronics for automation engineering or automotiveengineering. Devices of this type generally include a plurality ofindividual parts, such as printed circuit board assemblies or circuitcarriers, shielding plates or sheets, between which, during assembly(=when the individual parts are being joined together), a mechanicalconnection is to be created. Special demands, such as for example theprecise spacing and/or dissipation of heat both between the individualparts of the device and also of these individual parts with respect tofurther individual parts of the device, such as for example metal framesor shielding plates or sheets, are often also imposed on connections ofthis type. A corresponding electronic device is used as the basis forthe exemplary embodiment shown in the figures.

FIG. 1 shows the assembly state (=construction operation or phase) of adevice of this type, which is denoted overall by 2. This device has abase part 3 a of a housing 3 and two laterally arranged side parts 3 band 3 c. These housing parts, which consist, for example, of Al or steelsheet or plastic material, such as ABS, form a basic housing unit, whichis to be mounted with flat individual parts from its side which is openat the top. These individual parts may preferably be circuit carriers orprinted circuit board assemblies on which various electronic componentshave been mounted. The basis used for the exemplary embodiment is amodule board 4 a. These individual parts may equally well be shieldingplates or sheets, of which in the exemplary embodiment two shieldingpanels 4 b and 4 c are assumed to lie on the two (flat) sides of theboard 4 a. The large-area extent of these individual parts 4 a to 4 c ismatched to that of the housing base part 3 a. Within the housing unitcomprising parts 3 a to 3 c, they are stacked in a defined order withoutbeing locked or secured in the selected assembly or mounting direction,which is indicated by an arrow 5. Strip-like memory metal elements 6 iand spring-like memory metal elements 7 i are arranged on at least someof the panels, in the exemplary embodiment on the shielding panels 4 band 4 c, for example are soldered to the top side of the lower shieldingpanel 4 b and to the underside and top side of the upper shielding panel4 c. The memory metal elements 6 i and 7 i are in this case in apredetermined first form or configuration which does not interfere withassembly. Only after assembly are the memory metal elements to be usednot only to space the panels 4 a to 4 c apart from one another by adesired distance. Rather, they are also to be responsible for fixing thestack formed from these panels within the housing 3 which has beenclosed after assembly, i.e. at least in this state there should be apositive and preferably also nonpositive lock between the plate stack 4a to 4 c and the housing 3.

After the housing 3 has been closed using a housing cover part 3 d, inaccordance with FIG. 2 the memory metal elements 6 i and 7 i areactivated by a heat treatment with the aid of an associated heatingmeans. A heat treatment of this type is generally effected by anexternal increase in the temperature or by passing current through theelement. The current may also be passed through the individual panels insuccession. On account of this activation, the memory metal elementsthen adopt their second form or configuration, which was imparted tothem in a manner known per se before they were fitted to thecorresponding panel 4 b or 4 c. In FIG. 2, the memory metal elements 6 iand 7 i, after they have been activated, are denoted by 6 i′ and 7 i′,respectively. As can be seen from the figure, this second form of thememory metal elements 6 i′ and 7 i′ ensures a positive and nonpositivelock between respectively adjacent panels 4 a to 4 c and also betweenthe panels and the base part 3 a and the cover part 3 d of the housing3, i.e. the activation of the elements leads to self-aligning of themodule board 4 a and of the shielding plates or panels 4 b and 4 cwithin the housing 3 without any external mechanical intervention, inparticular at inaccessible locations, being required.

To dismantle the housing 3 in which the module 4 a and the shieldingpanels 4 b and 4 c have been mounted, the housing is opened, for exampleby the cover part 3 d being lifted off, and the side parts 3 b and 3 care removed sideways. In the process, the positive and nonpositive lockproduced by means of the memory metal elements 6 i′ and 7 i′ withrespect to these housing parts is eliminated; and the individual panels4 a to 4 c can now be removed for further use.

What this means is that a degree of dismantling which, for example,complies with statutory regulations and is suitable for replacement orretrofitting of functional components without additional outlay can beachieved after the housing parts have been opened, without anydestruction occurring.

The memory metal elements 6 i and 7 i at least partially comprise one ofthe known shape memory alloys. Examples of such alloys are Ti—Ni alloys,in which the Ti component and also the Ni component form the maincomponents and further alloying partners may also be present. Inaddition, there are also known Cu—Al alloys with further alloyingpartners in which the level of the Al component may be higher or lowerthan that of the further alloying partner. For example, “MaterialsScience and Engineering”, Vol. A 202, 1995, pages 148 to 156 disclosesTi—Ni and Ti—Ni—Cu alloys of various compositions.

“Intermetallics”, Vol. 3, 1995, pages 35 to 46 and “Scripta METALLURGICAet MATERIALIA”, Vol. 27, 1992, pages 1097 to 1102 describe specialTi₅₀Ni_(50−x)Pd_(x) shape memory alloys. Of course, other shape memoryalloys are also suitable as an alternative to the Ti—Ni alloys. Forexample, Cu—Al shape memory alloys are also suitable. A correspondingCuZn24A13 alloy is disclosed by “Z. Metallkde.”, Vol. 79, Issue 10,1988, pages 678 to 683. “Scripta Materialia”, Vol. 34, No. 2, 1996,pages 255 to 260 describes a further Cu—Al—Ni shape memory alloy.Further alloying partners, such as for example Hf, Pd, Au, Pt, Cr or ifappropriate Ti may also be added to the abovementioned binary or ternaryalloys in a manner which is known per se. By way of example, this atleast one further component forms less than 5 atomic %. However, thelevel of this at least one further component may also differ from thisvalue to a relatively great extent. Further possible alloying partnersfor various binary memory metals, including for Ni—Mn alloys, aredescribed in “Transactions of the ASME”, Vol. 121, Jan. 1999, pages 98to 101.

An Ni—Ti—Nb shape memory alloy can be selected for the exemplaryembodiment described above. Corresponding alloys are commerciallyavailable and, for example on the basis of their production process,have the following properties:

-   -   austenite temperature: >+50° C.;    -   martensite temperature: <−50° C.

Depending on the production process, it is possible to achievehysteresis ranges between −150° C. and +100° C. At a predetermined hightemperature of several hundred ° C., a desired high-temperature shape,which can be regarded as the second form of the element, is imparted toa corresponding memory metal element. When it cools to room temperature,this second form is converted into a starting shape (=first form; cf.FIG. 1). This starting shape of the memory metal element is the basicshape during assembly of the device.

If the element or a shielding plate or other component connected to itis then heated to a temperature which is above the Austenit temperatureof the memory metal, for example to 60 to 80° C., the element adopts thehigh-temperature shape (=second form; cf. FIG. 2) which was imparted toit. This second form is retained even after cooling back to roomtemperature and can only be reversed at lower temperatures (below theMartensit temperature) on account of the hysteresis property of thespecial metal.

Memory metals which use what is known as the one-way effect and what isknown as the two-way effect can be used for the elements (6 i, 7 i)according to the invention. An element with a one-way effect in itsmemory metal can remember its high-temperature shape which was impartedto it at a very high temperature of, for example, about 800° C. when theAustenit transition temperature, which is, for example, 60° to 80° C.,is exceeded. This high-temperature shape is then retained even in theevent of cooling to any desired lower temperature, e.g. to roomtemperature or below. However, a one-way effect element of this type canbe deformed by another actuator, such as for example a standard spring,in a low-temperature state, in particular below the Martensittransformation temperature. However, when it is heated it returns to thehigh-temperature shape which was imparted to it. On heating, an elementwith a two-way effect in its memory metal is also converted into thehigh-temperature shape which was imparted to it at a very hightemperature. By training, e.g. by being deformed 20 to 200 times in the,in relative terms, colder (e.g. unheated or recooled) state, the memorymetal adopts the shape into which it was trained when it is then cooleddown to what is known as the Martensit phase. The result of this is thata two-way effect element of this type is deformed differently as afunction of the temperature, namely into a high-temperature shape (e.g.when heated to over 80° C.) or into a low-temperature shape (e.g. whencooled to below −20° C.), i.e. depending on the temperature the two-wayeffect element automatically changes to the high-temperature shape whichwas imparted to it or to the trained low-temperature shape.

Both types of metal can be used for the elements according to theinvention, in particular if the housing is opened up for dismantling, sothat the individual modules, boards and plates are then exposed.Materials with a one-way effect then have a cost advantage. By contrast,elements made from a material of the two-way type return to theirstarting shape (=first form) when they are cooled strongly, so that theyeliminate a nonpositive lock produced in their assembled state evenwithout a housing having to be broken up.

1. An assembly of parts of an electronics device, comprising a firstpart of an electronics device; a second part of the electronics device;and a first memory metal element between said first and second parts;said first memory metal element having a first shape that permitsplacement of said first and second parts in the electronics deviceduring assembly of the electronics device, and a second shape that isdifferent from said first shape and that holds said first and secondparts in a locked position relative to each other in an assembled stateof the electronics device, said second shape being memorized in saidfirst memory metal element and existing after elevation of said firstmemory metal element above its austenite temperature, said first memorymetal element retaining said second shape and holding said first andsecond parts in the locked position after cooling said first memorymetal element below the austenite temperature and at an operatingtemperature of the electronics device.
 2. The assembly of claim 1,further comprising a third part of the electronics device and a secondmemory metal element between said second and third parts, said secondmemory metal element having a first shape that permits placement of saidthird part in the electronics device during assembly of the electronicsdevice, and a second shape that is different from said first shape andthat holds said second and third parts in a locked position relative toeach other in an assembled state of the electronics device, said secondshape being memorized in said second memory metal element and existingafter elevation of said second memory metal element above its austenitetemperature, said second memory metal element retaining said secondshape and holding said second and third parts in the locked positionafter cooling said second memory metal element below the austenitetemperature and at an operating temperature of the electronics device.3. An assembly of parts of an electronics device, comprising: a firstpart of an electronics device; a second part of the electronics device;and a first memory metal element between said first and second parts;said first memory metal element having a first shape that permitsplacement of said first and second parts during assembly of theelectronics device, and a second shape that is different from said firstshape and that holds said first and second parts in a locked positionrelative to each other in an assembled state of the electronics device,said first memory metal element being a metal that changes from saidfirst shape to said second shape upon elevation of said first memorymetal element to its austenite temperature and that thereafter retainssaid second shape to hold said first and second parts in the lockedposition at temperatures lower than the austenite temperature.